Sudden acceleration is also described by a variety of
other terms including "sudden unexplained
acceleration", "uncontrolled acceleration", "unintended
acceleration", "uncommanded acceleration", "runaway
vehicles", and, in an NBC TV report (NBC News/MSNBC,
Feb. 10, 1999), as "vehicles taking off on their
own". The picture presented is of a vehicle event in which
the throttle moves, apparently uncommanded, of its own
accord, rather mysteriously, to the fully open position,
without the driver pressing the accelerator pedal. In such
a situation the driver appears not to be able to exercise
any kind of control, except by switching off the ignition
or braking, which itself may be dangerous.

The US NHTSA [National Highways
Traffic Safety Administration ] provided the following
rather narrow definition of sudden acceleration from near
standstill in their 1989
Sudden Acceleration Report:

“Sudden acceleration
incidents” (SAI) are defined for the purpose of this
report as unintended, unexpected, high-power
accelerations from a stationary position or a very low
initial speed accompanied by an apparent loss of
braking effectiveness. In a typical scenario, the
incident begins at the moment of shifting to Drive” or
“Reverse” from “Park”.

The NHTSA definition appears to leave out of
consideration the following types of incidents :

any incident that might occur while the vehicle is
already in motion, for example:

a sudden acceleration from 20 to 60 mph, or 40 to
80 mph.

speed oscillations (hunting) about the set speed.

overshoot beyond a new set speed with the cruise
control on.

speed drift ( either up or down) with the cruise
control on.

sudden unexplained deceleration.

lurching

sudden accelerations when vehicle is pulling in to a
parking bay or stopping at traffic lights

incipient incidents -"near miss" incidents - when the
driver switched off the ignition, or managed to
apply sufficient brake pressure and brought the vehicle
to a halt safely.

alleged incidents of sudden acceleration in vehicles
with manual gearboxes. [These may result in a racing
engine, but it is likely that the driver's natural
reaction will be to disengage the clutch and then bring
the vehicle to a halt by controlled braking.]

For example:

some of the alleged sudden acceleration
incidents in Ford
Explorers reported in the UK by the Channel 4
programme in the Autumn of 2000 appear to be outside the
NHTSA definition, since (a) they mostly took place with
the vehicle already moving at speed and (b) in some
cases the vehicle was brought to a halt without causing
an accident and it could be argued that the driver had
managed to retain control of the vehicle.

Many sudden acceleration incidents reported in
vehicles fitted with electronic throttles occurred at
speed and therefore would be outside the NHTSA
definition. e.g the incident on 28th August 2009 when a
2009 Toyota Lexus
E350 driven by California Highways Patrol Officer
Mark Saylor experienced a serious malfunction that
caused the vehicle to accelerate when already at
road speed and which resulted in an accident in which
Saylor and the three other family members travelling
with him were killed.

In my opinion, any unexplained uncommanded
acceleration/deceleration event, at whatever speed and
whatever the duration, could possibly be a symptom of an
intermittent electronic control system malfunction.
Therefore, when an incident is investigated, the possibility
of an intermittent electronic malfunction should be
considered as one of a number of possible causes.

NHTSA in the 1989 Sudden Acceleration Report adopted a
set of 9 what they described as "logical assumptions" as the
basis for their study of sudden acceleration. The Report
recognised the possibility of intermittent electronic
malfunctions causing sudden accelerations but dealt with
them in a highly unorthodox manner eby means of the eighth
"logical assumption", which assumes the following
forensic methodology for the investigation of potential
intermittent electronic failures:

"If the cause of an SAI is an intermittent
electronic failure the evidence may be difficult to find
but the failure mode should be reproducible either
through in-vehicle or laboratory bench tests."

In my opinion, this is a
totally inappropriate basis for the diagnosis of
intermittent electronic malfunctions. I know of no
similar assumption being made anywhere in the electrical
and electronic engineering industries as part of a fault
diagnosis strategy.I know of no electrical engineer or technician
cognisant in any degree with electronic systems who
would dream of assuming that if he or she could not
reproduce an intermittent failure therefore it could
never have occurred.

Thisparticular
assumption,as
far as sudden acceleration diagnosis goes, has the
effect of re-classifying anyintermittent
electronic faults that fail to reproduce asproven
not to exist and, ergo, by fallacious argument, as an
instance of driver malfunction or "pedal error".

Since any sudden acceleration incidents that
could not be reproduced either through in-vehicle tests
or laboratory bench tests were deemed by NHTSA not to be
due to intermittent electronic failures, the following
conclusion in the 1989 Sudden Acceleration Report is
scarcely surprising:

“For SAI in
which there is no evidence of throttle sticking or
cruise-control malfunction, the inescapable conclusion
is that these definitely involve the driver
inadvertently pressing the accelerator instead of, or
in addition to the brake pedal.”

Absence
of proof is not proof of absence. In the
event of failing to reproduce a sudden acceleration
then the investigator must remain agnostic as to cause
and certainly not start reaching "inescapable
conclusions" as to the event being caused by the
driver.

Since
1989 when the NHTSA report was written, sudden
accelerations have continued to occur in sporadic
clusters. Manufacturers have continued to shelter behind
the report’s finding and blame drivers, or loose
floormats, or stuck throttles, for sudden accelerations.
Sudden accelerations still occur, sometimes with
disastrous results. In cases where there is death or
injury, by default the above "logical assumption"
regarding reproducibility leads inexorably the reversal
of the burden of proof, so that the vehicle, as a
general rule is, presumed ‘innocent’ i.e. not to have
malfunctioned, unless the driver can prove otherwise.

Why
the NHTSA should have adopted such a limiting definition
of a sudden acceleration is not at all clear. To an
outside observer, it appears that unexplained acceleration
in the automobile environment is being investigated on a
somewhat ad-hoc basis, with insufficient reference to
known art in control engineering theory and to standard
practice in control system fault diagnosis.

For example, if a competent electrical or control
engineer were investigating unexplained behaviour in a P
& I controller in an industrial application, they
would first seek to establish whether or not the system
response was within the design specification. To do this
they would of course have to know the key system design
parameters, which would have been provided to them, as a
matter of course, by the manufacturers. They would
normally measure the step and impulse responses of the
system and establish the gain/frequency response and
compare these with the design responses. They would inject
noise at critical points in the system. They would want to
see if the output drifted over time and if any parts of
the system could go into saturation and whether there were
any signs of instability. They might repeat the tests with
certain faults imposed on the control module. They would
also look for signs of poor electrical contact, electrical
tracking, hotspots, transient overvoltages and other
rather mundane causes of electrical misbehaviour. They
would, in other words, be carrying out a kind of
sensitivity analysis to establish how near the system was
to becoming unstable. They would be able to carry out this
investigatory process fairly effectively because most of
the relevant design information would have already been
made available to the owner of the equipment as a matter
of course as a very necessary part of the extent of
supply.

In the automobile industry things seem to be very
different. Almost all of the design information relating
to electronic systems - including details of
software and its updates - remains privy to the
manufacturer. The key information, which would allow
competent independent electrical or control system
engineers to critique safety-critical electronic systems,
is kept securely under wraps and can only be obtained by
the lengthy, inefficient and costly process of legal
discovery. Effectively the automobile industry is
self-certifying and customers have no independent
way of assessing whether or not safety critical
products meet essential requirements for functional safety
either when they purchase the vehicle or thereafter.

In my opinion, this is a thoroughly unsatisfactory
situation: taking the manufacturer's word for the
functional safety of what are now highly complex
safety-critical electronic systems is no longer
acceptable. Protocols need to be put in place, as in other
industries, that allow independent evaluation of
safety critical automobile systems at the design stage so
that the customer can have confidence that the systems
have been designed, manufactured and installed in
accordance with best current functional safety
practice.